The present invention relates to a method of manufacturing an aluminum-stabilized superconducting wire having a high thermal and electrical stability, being resisting to deformation caused by an electromagnetic force generated when employed as a magnet or the like, and having a sufficient mechanical strength, at high productivity.
A superconducting wire is manufactured by embedding a superconducting filament such as an Nbxe2x80x94Ti alloy in a copper or copper-alloy matrix, and providing, usually, a coating of copper as a stabilizer, on its outer circumference.
Recently, an aluminum-stabilized superconducting wire which uses, as a stabilizer, high purity aluminum which has a residual resistance ratio (the ratio of the electrical resistance value at 300 K to that at 10 K) much larger than that of copper has been developed. It should be noted that the residual resistance ratio is an index for the thermal and electrical stability.
Since a density of aluminum is low as about ⅓ of that of copper, the aluminum-stabilized superconducting wire enables to lighten the magnet or the like. Further, since aluminum is superior in terms of elementary particle permeability to copper, the aluminum-stabilized superconducting wire can be advantageously applied for a magnet used for detect elementary particles, which is widely used in the field of high-energy physics.
Such an aluminum-stabilized superconducting wire is manufactured by a method in which aluminum is quickly heated to a temperature of about 350 to 550xc2x0 C. by induction heating or frictional heat generation, and extruded and applied on the circumference of a superconducting wire such as a single core super-conducting wire or multiple core superconducting wire.
Meanwhile, in a large-size magnet, a strong electromagnetic force is applied to a superconducting wire. Consequently, an aluminum-stabilized superconducting wire, which uses high purity aluminum, may be deformed by such an electromagnetic force. Here, it is considered as one solution that an aluminum-stabilized superconducting wire is cold-worked so as to harden the aluminum stabilizer. However, as to a high purity aluminum stabilizer, even if it is cold-worked, the mechanical strength cannot be markedly improved.
Under these circumstances, a method of using a stabilizer formed of an aluminum alloy in place of high purity aluminum, has been considered.
However, of the aluminum alloys, a solid-solution type aluminum alloy to which a solid-solution type element such as Cu, Zn, Si or Mg has been added, is of a type that the arrangement lattice of aluminum atoms is distorted by solid-solution element, in order to reinforce the aluminum alloy, and therefore it is necessary to dissolve a great amount of alloy elements in order to achieve a high strength. However, if a great amount of solid-solution elements are added, the conductivity is significantly lowered. Therefore, it is very difficult to achieve both a high strength and high conductivity at the same time.
Meanwhile, as to precipitation-type aluminum alloys to which Ni has been added, the solubility limit of Ni with respect to aluminum is extremely low, and therefore most of Ni added will form an intermetallic compound together with Al while solidifying, which precipitates as primary crystal, thereby contributing to the enhancement of the strength, whereas a little amount of the remainder dissolves in a supersaturated manner, thereby decreasing the conductivity significantly.
As a method of age-precipitating such a supersaturated solid-solution element, there is a technique of age-precipitation achieved through a heat history in the extruding machine by decreasing the extrusion rate at the time of hot extrusion coating; however it has a poor productivity and therefore is not practically applicable. Further, it entails a problem that the xcex1-Ti precipitates and introduced dislocations in the Nbxe2x80x94Ti filament disappear due to the heat history in the low-speed extrusion, thereby deteriorating the magnetic flux pinning effect and lowering the magnet property.
Further, there is another method of aging treatment carried out after extrusion covering; however this method also entails a problem that the xcex1-Ti precipitates and introduced dislocations disappear, thereby deteriorating the magnet property.
Under these circumstances, the inventors of the present invention conducted intensive studies on methods of enhancing the conductivity of an aluminum stabilizer which uses a precipitation-type aluminum alloy without lowering the productivity or deteriorating the magnet property. They found that the conductivity of the stabilizer could be improved by performing extrusion covering after carrying out a predetermined aging treatment on a precipitation-type aluminum alloy, and conducted further studies, thus achieving the present invention.
Therefore, the object of the present invention is to provide a method of manufacturing an aluminum-stabilized superconducting wire having a high thermal and electrical stability, being resisting to deformation caused by an electromagnetic force generated when employed as a magnet or the like, and having a sufficient mechanical strength, at high productivity.
According to the present invention, there is provided a method of manufacturing an aluminum-stabilized superconducting wire, comprising the step of hot-extrusion-coating an entirety or a part of an outer circumference of a superconducting wire which includes a superconducting filament embedded in a copper or copper-alloy matrix, with a stabilizer made of a precipitation-type aluminum alloy, wherein the precipitation-type aluminum alloy is an Alxe2x80x94Ni alloy containing 100 to 25000 ppm of Ni, and the stabilizer made of the precipitation-type aluminum alloy is subjected prior to the hot extrusion coating step, to an aging-heat treatment in which it is heated at a temperature of 250xc2x0 C. to 500xc2x0 C. for 10 minutes or more.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.